A displacement sensor using an oscillator circuit has been known as a displacement sensor that measures the distance to a measurement target such as metal. In the displacement sensor, an oscillator circuit and an integrating circuit are mounted on a board that has a coil. In the displacement sensor, because the oscillation frequency of the oscillator circuit varies in accordance with the change in the distance between the coil and the measurement target, the distance to the measurement target is measured by detecting the oscillation frequency.
Because such a sensor radiates harmonics (noise), it must meet standardized EMC (electromagnetic compatibility) standards. For that reason, in the environment in which a displacement sensor has been used, the entire sensor, including the measurement target, needed to be shielded, so that the harmonics radiated by the displacement sensor did not leak to the outside. However, in the method of shielding the entire displacement sensor in this manner, there have been cases in which the shielding material cost and manufacturing cost and the like increased. Also, depending upon the environment in which the displacement sensor is used, there have been cases in which it was not possible to shield the entire displacement sensor. If a constituent element (noise-reduction means) is provided within the circuit in order to reduce the harmonics, not only the harmonics, but also the fundamental waveform used in distance measurement is affected. For that reason, in the displacement sensor field the provision within the displacement sensor of an element to reduce harmonics has not been done. Also, in a displacement sensor using an LC oscillator circuit, if measurement is done using an oscillation frequency in the order of megahertz, the strengths of both the fundamental waveform used in measurement and the harmonics increase, so that there have been cases in which it was difficult to meet EMC standards.